Turbine motor of a rotary atomizer

ABSTRACT

A turbine, e.g., with a blade arrangement, which receives an air flow in the radial direction and which is located on a carrier surface of the turbine wheel, is used as a drive motor for a rotary atomizer. The drive channel, which contains the turbine blades and which is limited by the carrier surface, is also closed on its other side by a cover element, which is attached to the turbine wheel and which rotates with the wheel for increasing efficiency. For an additional increase in efficiency, the inlet for the drive air of the turbine is configured as an ultrasonic nozzle with a cross section that expands continuously up to the opening.

PRIOR APPLICATIONS

[0001] This application claims priority to German Patent Application No.DE 102 33 199.5 filed Jul. 22, 2002.

FIELD OF THE INVENTION

[0002] The invention concerns a turbine motor that can be used as thedrive for the bell-shaped Plate of a rotary atomizer according to thepreamble of claim 1. More specifically, it concerns high-speed rotaryatomizers for the electrostatic mass-production coating of workpieces,such as vehicle chassis.

BACKGROUND

[0003] Radial turbines, which are operated in a known way withcompressed air and which have a hollow shaft that carries thebell-shaped plate and that rotates in an air bearing, are used fordriving the bell-shaped plate of such atomizers (DE 43 06 80, EP 0 796663 B1). Air can either flow against the radial turbines in thetangential direction or through the turbines in the radial direction. Inthe latter case, the turbine wheel consists of a disk, which rotates inan essentially closed cylindrical interior of the bearing unit of thedrive shaft and which has turbine blades formed on its end surface nearthe periphery. The driving air flows through the turbine blades in theradial direction within a channel, which is limited on one side by theturbine wheel and, in the known case, on its opposite side by astationary part of the bearing unit. The driving air is guided into thisdrive channel through one or more supply channels, which open into anozzle, whose opening, e.g., with a rectangular cross section,represents in the known case the smallest cross section of theassociated driving-air supply. There is an air gap between the axialends of the turbine blades and the stationary part of the bearing unitthrough which a portion of the driving air for the drive is lost.Another disadvantage is a turbulent boundary layer, which forms betweenthe flowing driving air and the stationary housing part for theconsidered known radial turbine and causes high friction losses.Consequently, the efficiency of the known radial turbine is limited.

SUMMARY OF THE INVENTION

[0004] The invention is based on the problem of providing a turbinemotor for a rotary atomizer, which enables a higher driving efficiencythan for comparable, known radial turbines.

[0005] This problem is solved by the turbine motor characterized in theclaims.

[0006] The turbine is significantly improved by the invention in termsof flow. In particular, because the drive channel is not limited on onlyone side as before, but instead is also closed on the other side by anelement that rotates with the turbine, the drive air can flow throughthe closed channel without losses and with low friction. An advantageouspossibility for realization is to limit the drive channel by a disk,which is attached to the turbine wheel and/or to the drive shaft, whichrotates with the wheel, and which can form or contain at least oneoutlet opening for the driving air on the inside in the radialdirection.

[0007] According to another feature of the invention, thecross-sectional area of the inlet opening through which the driving airflows from a supply channel of the bearing unit into the drive channelof the turbine should be greater than the cross-sectional area of thesupply channel at its point of smallest cross section. In particular,the inlet can be configured as a so-called Laval or ultrasonic nozzle,whose cross section first narrows and then expands to generate gas flowrates that can lie, at least theoretically, in the ultrasonic range.Surprisingly, it has been determined that the resulting changes in speedand pressure of the incoming air lead to a significant improvement ofthe driving efficiency of the turbine in comparison with the previouslyconventional nozzles.

[0008] The turbine can be optimized in terms of flow by the invention,which can provide, above all, a higher rpm than before. For a rotaryatomizer, a higher outflow rate of the coating material at thebell-shaped plate driven by the turbine is achieved with the higher rpm.

[0009] Preferably, the mass of the entire exchangeable motor unit(without bell-shaped plate), known as a modular-type construction unit,is less than 0.8 kg, which was previously possible only forsignificantly lower-power turbines of the considered class.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Other advantages of the present invention will be readilyappreciated as the same becomes better understood by reference to thefollowing detailed description when considered in connection with theaccompanying drawings wherein:

[0011]FIG. 1 shows a section through the bearing unit of a rotaryatomizer along the axis of the drive shaft in a schematically simplifiedillustration.

DETAILED DESCRIPTION OF THE INVENTION

[0012] The bearing unit forming the turbine motor described here has astationary housing 1, in which the drive shaft 2 rotates in an airbearing formed between the housing and the shaft. The disk-shapedturbine wheel 3 is arranged at one end of the drive shaft 2. The ring ofturbine blades 5 for flow in the radial direction is formed on anannular area of the axial end surface 4 of the turbine wheel facing theshaft lying near the periphery of the disk. The turbine wheel 3 rotatesin a cylindrical interior 6 of the housing 1 dimensioned correspondingto the turbine wheel with walls adjacent to the rear flat end surface 7and the cylindrical peripheral surface 8 of the turbine wheel. On theopposite side, on the left in the drawing, the interior 6 is limited byanother wall surface of the stationary housing 1 running in the radialdirection, which forms the opening for the shaft 2 in the center andwhich is positioned, outside of this opening, opposite the axial endsurface 4 of the turbine wheel 3 at the illustrated axial distance fromthe ends of the turbine blades 5 in the radial direction. Outside of thecircumference of the turbine wheel 3 in the radial direction and alignedwith the turbine blades 5 in the axial direction, an inlet 10 opens intothe interior 6 for the drive air of the turbine, which comes out of asupply channel running through the housing 1. Another air inlet can beprovided at 10′. Typically, the housing 1 contains separate inlets fordriving air and braking air (EP Application No. 02006826.8). The driveshaft can be configured as a hollow shaft and the (not-illustrated)bell-shaped plate of the rotary atomizer is screwed into the other endof the drive shaft.

[0013] As described thus far, the illustrated bearing unit cancorrespond to the state of the art of conventional rotary atomizers.However, according to the invention, a circular ring-shaped cover disk12 is attached to the turbine wheel 3 on the side of the end surface 4.This cover disk directly contacts to the ends of the turbine blades 5projecting from the end surface 4 in the axial direction and rotateswith the blades. To explain the differences from the state of the art,only its top half is illustrated. The cover disk 12 can be adhered,welded, or attached in some other way, e.g., to the ends of the turbineblades 5 extending in the axial direction. Thus, a drive channel 13closed in the axial direction on both sides of the turbine blades 5 isformed between the end surface 4 and this cover disk 12, in which thecompressed air, which is fed from the air inlet 10 in a direction thatis at least approximately tangential and if necessary with a componentdirected inwards in the radial direction, flows without loss and withlow friction between the turbine blades. The air released after thedelivery of the drive energy to the shaft flows within the annularsurface area containing the turbine blades in the radial direction intoone or more recesses 15 and channels 16 of the housing 1 acting as airoutlets.

[0014] It is conceivable to provide turbine blades in the described,closed drive channel not only on one side, but also on both sides of theturbine wheel. Likewise, it is possible to arrange more than just oneturbine on a common shaft.

[0015] The cross-sectional area of the opening at the air inlet 10, thusat the outlet point of the drive air, is preferably greater than thesmallest cross section of the upstream channels of the bearing unit, inwhich the drive air is guided in a known way through at least one holein an annular segment-shaped supply channel and from this channel intoone or more nozzles. In contrast to conventional nozzles with a crosssection that narrows constantly up to the opening, which can acceleratethe flowing medium only up to a speed that is less than the speed ofsound, the air inlet 10 is configured as a Laval nozzle, e.g., whosecross section first narrows and then expands up to the opening in orderto generate ultrasonic speeds in the expanded nozzle section. Suchultrasonic nozzles can be advantageous not only for the radial turbinesdescribed here, but also for other types of turbine motors in order toincrease the efficiency.

[0016] The described embodiment can be modified in various ways withinthe scope of the invention. If the turbine wheel consists of two diskelements that are separated in the axial direction, these can beconnected by axial crosspieces, e.g., at the periphery, between whichthere are open passage openings for air flow, so that the drive channelformed between the disk elements is partially closed also at theperiphery of the turbine wheel. Furthermore, instead of inside one ofthe disk elements in the radial direction, the outlet for the drive aircan be located at any other arbitrary position and, if necessary, alsooutside of the turbine wheel in the radial direction.

[0017] In addition, the invention is limited neither to the describedtangential or radial direction of incoming air nor to two spatiallyseparated disks nor to a certain shape of the blade elements. Forexample, the blade elements can be arranged between a closed cylindricalsurface at the periphery of the turbine wheel and an inner, similarlyclosed and cylindrical surface that is spatially separated from theother surface in the radial direction, so that a drive channel limitedin the radial direction on two sides is formed, with the blade elementsreceiving air flow in the axial direction and with air outlets beingable to be located at the opposite end of the annular drive channel inthe axial direction.

[0018] The invention has been described in an illustrative manner, andit is to be understood that the terminology which has been used isintended to be in the nature of words of description rather than oflimitation.

[0019] Obviously, many modifications and variations of the presentinvention are possible in light of the above teachings. It is,therefore, to be understood that within the scope of the appendedclaims, wherein reference numerals are merely for convenience and arenot to be in any way limiting, the invention may be practiced otherwisethan as specifically described.

1. A turbine motor for use as a drive for a bell-shaped plate of arotary atomizer comprising: a housing; a drive shaft of said motor ahaving a bearing unit; a turbine wheel drivably arranged upon said driveshaft rotatably disposed within a drive channel of said housing andhaving blade elements disposed upon a carrier surface; an inlet forproviding a driving gas through said housing and into driving contactwith said blade elements of said turbine wheel; and a shielding elementpositioned adjacent said blade elements thereby limiting said drivechannel.
 2. A turbine motor according to claim 1, wherein said turbinewheel is formed by two disk elements lying in an opposed relationship inan axial direction and being limited by said drive channel.
 3. A turbinemotor according to claim 1, wherein said shielding element comprises adisk operably connected to one of said drive shaft and said turbinewheel thereby rotating with said turbine wheel.
 4. A turbine motoraccording to claim 1, wherein said shielding element is fixedly attachedto said turbine blades.
 5. A turbine motor according to claim 1, whereinsaid shielding element is welded to said turbine blades.
 6. A turbinemotor according to claim 1, wherein said shielding element defines atleast one outlet for said driving gas.
 7. A turbine motor according toclaim 1, wherein said inlet for driving gas is positioned in saidhousing spaced from said drive shaft in a radial direction.
 8. A turbinemotor according to claim 6, wherein said opening defined by saidshielding element includes a cross-sectional area greater than asmallest cross-sectional area of said inlet.
 9. A turbine motoraccording to claim 8, wherein said inlet is configured as a Laval nozzlehaving a cross-section expanding after narrowing adjacent said openingleading into the drive channel.